The present invention relates to proppants and the use of proppants for hydrocarbon recovery, such as in subterranean formations. The present invention further relates to identifying one or more desirable properties in a proppant and methods for screening or selecting such proppants, as well as methods to improve one or more properties in the use of proppants in treating a subterranean producing zone.
Proppants are materials pumped into oil or gas wells at extreme pressure in a carrier solution (typically brine) during the hydrofracturing process. Once the pumping-induced pressure is removed, proppants “prop” open fractures in the rock formation and thus preclude the fracture from closing. As a result, the amount of formation surface area exposed to the well bore is increased, enhancing recovery rates. Sand is the most commonly used proppant due to its availability and low cost, but sand has limitations, such as its low crush strength and agglomeration problems, settling, and the ability to achieve deep placement of the sand in the desirable locations in the well bore or fractures thereof.
Ceramic proppants are becoming widely used as propping agents to maintain permeability in oil and gas formations. High strength ceramic proppants have been used in the hydrofracture of subterranean earth in order to improve production of natural gas and/or oil. For wells that are drilled 10,000 feet or deeper into the earth, the proppant beads need to withstand 10 kpsi or higher pressure to be effective to prop the fracture generated by the hydrofracture process. Currently only proppants formed from high strength materials, such as sintered bauxite and alumina have sufficient compressive and flexural strength for use in deep wells. These conventional high strength materials are expensive, however, because of a limited supply of raw materials, a high requirement for purity, and the complex nature of the manufacturing process. In addition, such high strength materials have high specific gravity, in excess of 3.0, which is highly undesirable for proppant applications. Producing high strength proppants with low specific gravity is also a challenge. In field applications, the transportability of proppants in wells is hindered by the difference of specific gravities of proppant and carrying fluid. While light weight oxide materials, such as cordierite, have low specific gravity, they have a relatively weak flexural strength and stiffness.
In conventional proppant technology, the key parameters that were considered key for proppant success were crush strength, specific gravity, chemical resistance to the subterranean formation, the fluids used in the subterranean formation, and particle size. However, when these properties were achieved or nearly achieved, the success of the proppant in the subterranean formation still had significant room for improvement with respect to controlling settling velocity, reducing agglomeration, avoiding pressure drops in the formation, obstruction of the proppants along the well bore and walls, bridging, clogging, and the like. Thus, the inventors of the present invention realized that other key parameters of the proppant must not be present in view of these undesirable properties that were still occurring with regard to the proppant in the subterranean formation. Thus, there was a need to develop more improved proppants, methods for selecting proppants, and methods for improving one or more of the above-identified properties which were not being achieved with conventional proppants.